Generally, a broadband wireless access system supports an idle mode and a sleep mode to minimize power consumption of a mobile subscriber station (MSS). The mobile subscriber station includes a mobile subscriber station applicable to a communication system enabling handover or a mobile subscriber station enabling wireless communications within an area covered by an access point.
During an idle mode, a mobile subscriber station needs not to perform a handover procedure in moving between base stations (BS) included in a same paging zone. The mobile subscriber station needs not to perform uplink information transmission for the handoff procedure, thereby saving the corresponding power consumption.
Actions of the idle mode can be summarized as follows. A paging zone is defined as an entire area taken charge of by a plurality of base stations called a paging group. Base stations included in the same paging zone have the same paging cycle (Paging_Cycle) and paging offset (Paging_Offset).
A mobile subscriber station can make a request for entering an idle mode to a base station. The base station delivers its paging zone ID (Paging-group ID) and the corresponding paging cycle and offset, whereby the mobile subscriber station can enter the idle mode. In entering the idle mode, the mobile subscriber station delivers a list the base station intends to retain in a format of flag. The base station delivers the information to retain in a format of flag in delivering the paging cycle and the paging offset. The retained information can be retained/managed by the base station having allowed the idle mode or by a paging controller as another object.
During the idle mode, the mobile subscriber station can decide whether to retain or end the idle mode through a paging delivered in a broadcast form from the base station each negotiated paging cycle. The mobile subscriber station performs a location update. The location update is performed if the paging group is changed or if an idle mode timer expires.
If a traffic to be transmitted by the mobile subscriber station in idle mode is generated, the mobile subscriber station can end the idle mode at any time. Meanwhile, if a traffic to be delivered to the mobile subscriber station in idle mode is generated, the base station enables the mobile subscriber station to end the idle mode via paging. If the mobile subscriber station is unable to receive the paging at a determined time since the mobile subscriber station in idle mode moves away into another paging zone or loses its synchronization or the like, the mobile subscriber station ends the idle mode.
Namely, as long as there is no information to transmit or receive, the mobile subscriber station having entered the idle mode can secure its free mobility within the same paging zone by receiving the paging periodically without performing a handoff procedure.
A mobile subscriber station enters an idle mode in a following manner. To enter an idle mode, a mobile subscriber station forwards an idle mode request message to a serving base station. The serving base station delivers a paging group ID, a paging cycle and a paging offset value to the mobile subscriber station via an idle mode response message and releases connection information with the mobile subscriber station and a radio resource allocated to the mobile subscriber station and the like.
Table 1 is an example of an idle mode requesting message from a mobile subscriber station to a base station using a conventional deregistration request message.
TABLE 1SyntaxSizeNotesDREG-REQ message_format( ){Management Message Type =8 bits49De-8 bits0x00: MSS de-registration_Request_Coderegistration requestfrom BS and network0x01: Request for MSSde-registration fromServing BS andinitiation of MSS idlemode0x02-0x020xFF:reservedTLV encoded parametersVariable}
If a De-registration_Request_Code of the deregistration request message (DREG-REQ) is set to 0x01 (idle mode initiation request), information, as shown in Table 2, is included in the deregistration request (DREG-REQ) message to be transmitted to a mobile subscriber station. Table 2 shows an example of TLV encoding of a deregistration request (DREG-REQ) message.
TABLE 2NameTypeLengthValuePaging Cycle?2Request cycle in which theRequestpaging message is transmittedwithin the paging group.Idle Modem1MSS request for PagingRetainController retention of networkinformationre-entry MAC management messageMXX service and operationalinformation to expedite futureNetwork Re-entry from Idle Mode.For each Bit location, a valueof ‘0’ indicates the informationassociated with the specifiedMAC management message is norequested to be retained andmanaged, a value of ‘1’indicates the information isrequested to be retained and managed.Bit #0: Retain MSS service andoperational informationassociated with SBC_REQ/RSP MACmanagement messagesBit #1: Retain MSS service andoperational informationassociated with PKM-REQ/RSP MACmanagement messagesBit #2: Retain MSS service andoperational informationassociated with REG-REQ/RSP MACmanagement messagesBit #3: Retain MSS service andoperational informationassociated with NetworkBit #4: Retain MSS andoperational informationassociated with Time of DayAcquisitionBit #5: Retain MSS service andoperation information associatedwith TFTP MAC managementmessagesBit #6: Retain MSS service andoperational informationassociated with Full service(MAC state machines, CSclassifier information, etc.)
Table 3 shows an example of an idle mode response message forwarded from a base station to a mobile subscriber station using a conventional deregistration command (DREG-CMD) message.
TABLE 3SyntaxSizeNotesDREG-CMD_Message_Format( ) {Management Message Type = 298 bitsAction code8 bitsTLV encoded parametersVariable}
Table 4 shows examples of action codes of a conventional de-registration command (DREG-CMD) message.
TABLE 4ActionCodeAction0x00MSS shall leave the current channel andattempt to access another channel0x01MSS shall listen to the current channelbut shall not transmit until an RES_CMDmessage of DREG_CMD with Action Code 0x00is received.0x02MSS shall listen to the current channelbut only transmit on the Basic, PrimaryManagement, and Secondary ManagementConnections.0x03MSS shall return to normal operations andmay transmit on any of its activeconnections.0x04MSS shall terminate current NormalOperations with the BS: the BS shalltransmit this action code only in responseto any SS DREG_REQ.0x05Require MSS de-registration from ServingBS and request initiation of MSS idlemode.0x06The MSS may retransmit the DREG_REQmessage after the time duration (REQ-duration) given by.0x07The MSS shall not retransmit the DREG_REQmessage and shall wait for the DREG-CMDmessage.0x08-0xFFReserved
If an action code of deregistration command (DREG-CND) is set to 0x05 (idle mode permission), the following information is included in a deregistration command (DREG-CMD) message to be forwarded to a mobile subscriber station.
Table 5 shows an example of TLV encoding of deregistration command (DREG-CMD).
TABLE 5NameTypeLengthValuePaging?4Bits 15:0 - PAGING_CYCLE - Cycleinformationin which the paging message istransmitted within the paging group.Bits 23:16 - PAGING OFFSET -Determines the frame within thecycle in which the pagingmessage is transmitted. Must besmaller than PAGING CYCLE value.Bits 31:24 - Paging group theMSS is assigned to.REQ-duration?1Waiting value for the DREG-REQmessage re-transmission (measurein frames)Pagingoo6This is a logical networkControlleridentifier for the serving BS ofIDother network entity retainingMSS service and operationalinformation and/or administeringpaging activity for the MSSwhile in IDLE mode.Idle Modepp1Idle Mode Retain information isRetainprovided as part of this messageinformationis indicative only.Network Re-entry from idle modeprocess requirements may changeat time of actual re-entry. Foreach bit location, a value of‘0’ indicates the informationfor the associated re-entrymanagement messages shall not beretained and managed, a value of‘1’ indicates the informationfor the associated re-entrymanagement message shall beretained and managed.Bit #0: retain MSS service andoperational informationassociated with SBC_REQ/RSP MACmanagement messagesBit #1: Retain MSS service andoperational informationassociated with PKM-REQ/RSP MACmanagement messagesBit #3: Retain MSS service andoperational informationassociated with NetworkBit #4: Retain MSS andoperational informationassociated with Time of DayBit #5: Retain MSS service andoperation information associatedwith TFTP MAC managementmessagesBit #6: Retain MSS service andoperational informationassociated with Full service(MAC state machines, CSclassifier information, etc.)
A base station notifies a medium access control (hereinafter abbreviated ‘MAC’) of a mobile subscriber station entering an idle mode to other base stations of a paging group to which the corresponding base station belongs to enable the corresponding mobile subscriber station to be paged by a same paging cycle (PAGING_CYCLE, PAGING OFFSET).
The mobile subscriber station having been permitted to enter the idle mode via the idle mode response message decides whether there is a downlink traffic delivered to itself via a broadcast-formatted paging message delivered from the base station, whether to perform a ranging or whether to keep retaining the idle mode, according to the paging cycle.
Table 6 shows an example of a paging announce (Paging-announce) message, which is forwarded to a paging controller or all base stations within a same paging zone by a base station having approved an idle mode entry of a mobile subscriber station.
TABLE 6FieldSizeNotesMessage Type 8bitsSender BS-ID48Base station unique identifierbits(Same number as that broadcastedon the DL-MAP message)Recipient BS-48Set to 0xffffff to indicateIDbitsbroadcastTime Stamp32Number of milliseconds sincebitsmidnight GMT (set to 0xffffffff toignore)Num MSS 8Number of MSSs to pagebitsFor(j=0;j<Num MSS;j++) {MSS MAC48addressbitsPaging Group 8The identifier of the paging groupIDbitsto which the MSS belongsPAGING CYCLE16MSS PAGING CYCLE parameterbitsPAGING OFFSET 8MSS PAGING OFFSET parameterbitsAction Code 30: MSS enters Idle Modebits1: MSS exists Idle Mode2: MSS should be paged to performranging to establish location andacknowledgement message3: MSS should be paged to enter anetworkreserved 5bits}SecurityTBDA means to authenticate thisfieldmessageCRC field32IEEE CRC-32bits
Optionally, in forwarding the message, the base station having approved the idle mode forwards the paging announce message to the paging controller. The paging controller generates a differently-formatted message based on the contents and then forwards it to all base stations within the same paging zone.
Table 7 shows an example of a paging message periodically received by a mobile subscriber station from base stations of a paging group.
TABLE 7SyntaxSizeNotesMOB_PAG-ADV_Message_Format( ) {Management Message 8 bitsType=??Num_Paging_Group_IDs 8 bitsNumber of PagingGroup IDs in thismessageFor(i=0;i<Num_Paging_Group_IDs;I++ {Paging Group ID 8 bits}For(j=0;  j<Num  _MACs;Number of MSS MACj++) {Addresses inmessage can bedetermined from thelength of themessage (found inthe generic MACheader).MSS MAC Address hash24 bitsThe hash isobtained bycomputing a CRC24on the MSS 48-bitMAC address. Thepolynomial for thecalculation is0x864CFB.Action Code 2 bitsPaging actioninstruction to MSS:00 = No ActionRequired;01 = PerformRanging toestablish locationand acknowledgemessage;10 = Enter Network;and11 = ReservedReserved 6 bits    }}
Once the mobile subscriber station receives the paging message indicating that there is a downlink traffic, the mobile subscriber station terminates the idle mode and re-registers to a network to receive a downlink data traffic. In case of performing re-registration to the network after terminating the idle mode, the mobile subscriber station re-registers to the network using ranging.
Table 8 shows an example of a ranging request (RNG-REQ) message.
TABLE 8SyntaxSizeNotesRNG_REQ_Message_Format( ) {Management Message Type = 48 bitsDownlink Channel ID8 bitsTLV Encoded InformationvariableTLV specific}
Table 9 shows information added to a ranging request when a mobile subscriber station conducts a location update or re-registers to a network after terminating an idle mode. A base station having received this information recognizes that the mobile subscriber station performs ranging to make the location update in idle mode or the re-registration to the network.
TABLE 9Serving BS46The unique identifier of the formerIDServing BSHO1Presence of item in message indicates theIndicationMSS is currently attempting HO to the BSregardless of valueHO ID51The identification assigned to a MSSduring HO by a target BSLocation1Presence of item in message indicates MSSUpdateaction of Idle Mode Location UpdaterequestProcess, regardless of valuePaging6This is a logical network identifier forControllerthe serving BS or other network entityIDretaining MSS service and operationalinformation and/or administrating pagingactivity for the MSS while in Idle Mode
In re-registering to the network quickly from the idle mode using ranging, the base station or paging controller firstly approved the idle mode informs the mobile subscriber station of the currently retained information to instruct a procedure that can be skipped by the mobile subscriber station. The mobile subscriber station performs quick network re-registration by performing a necessary procedure only using the information. If the mobile subscriber station is requested to perform ranging by the paging message, the mobile subscriber station performs the ranging so that the base station can update a location of the mobile subscriber station and a valid idle mode mobile subscriber station list.
Table 10 shows an example of a ranging response message transmitted in response to the ranging response message.
TABLE 10SyntaxSizeNotesRNG_RSP_Message_Format( ) {Management Message Type = 58 bitsDownlink Channel ID8 bitsvariableTLV specific}
Table 11 shows a ranging response (RNG-RSP) TLV message.
TABLE 11HO Process1For each Bit location, a value of ‘0’Optimizationindicates the associated re-entrymanagement message shall be required, avalue of ‘1’ indicates the re-entrymanagement message may be omitted.Regardless of the HO ProcessOptimization TLV settings, the Target BSmay send unsolicited SBC-RSP and/or REG-RSP management messages.Bit #0: Omit PKM-REQ RSP managementmessages during current reentry processingBit #1: Omit PKM-REQ RSP managementduring current reentry processingBit #3: Omit Network Address Acquisitionmanagement messages during currentreentry processingBit #4: Omit time of Day Acquisitionmanagement messages during currentreentry processingBit #5: Omit TFTP management messagesduring current reentry processingBit #6: Full service and operationalstate transfer or sharing betweenServing BS and Target BS (ARQ, timers,counters, MAC state machines, etc.)Bit #7: post-HO reentry MSS DL dataprocessing at Target BSHO IDThe identifier assigned to a MSS duringHO by a target BSLocation0x00: Failure of Location Update, TheUpdateMSS shall perform Network Reentry fromIdle Mode.0x01: Success of Location update0x10, 0x11: ReservedPagingPaging information shall be only beInformationincluded if Location Update Response = 0x01and if Paging Information has changed.Bits 15:0 - PAGING CYCLE - Cycle in whichthe paging message is transmitted withinthe paging groupBits 23:16 - PAGING OFFSET - Determinesthe frame within the cycle in which thepaging manage is transmitted. Must besmaller than PAGING CYCLE valueBits 31:24 - Paging Group ID - ID of thepaging group the MSS is assigned toPagingThis is a logical network identifier forController IDthe serving BS or other network entityretaining MSS service and operationalinformation and/or administrating pagingactivity for the MSS while in Idle Mode.Paging Controller ID shall only beincluded if Location Update Response = 0x01and if Paging Controller ID has changed.
The ranging response (RNG-RSP) TLV message is the information added to the ranging response when the mobile subscriber station re-registers to the network after having made the location update or after having terminated the idle mode. Though this, the base station notifies the mobile subscriber station of the valid information retained by the network so that the mobile subscriber station can know the procedures that can be omitted in performing the network re-registration.
Besides the above-explained method, the mobile subscriber station performs location update through ranging at a time point corresponding to an update condition. In doing so, the mobile subscriber station uses the messages shown in Table 7 and Table 8. The location update condition includes a case when a paging zone is changed, a case when a timer expires and the like.
If the forwarded paging message instructs not to do any activity, the mobile subscriber station maintains the idle mode without doing a specific activity. If the mobile subscriber station terminates the idle mode since an uplink or downlink traffic of the mobile subscriber station is generated or since the mobile subscriber station moves away into another base station belonging to a different paging group, the base station informs other base stations belonging to the same paging group of such a fact so that they can delete the corresponding mobile subscriber station from the idle mode mobile subscriber station list.
In the related art, the mobile subscriber station enables the base station or the paging controller to retain the information of the mobile subscriber station. In particular, an IP address of the mobile subscriber station is made to be retained. In case that the IP address needs to be updated due to the variation of an IP subnet or a foreign agent after transition to the idle mode, the mobile subscriber station detects this only by the periodic location update with the base station and then updates the IP address.
Hence, it is unable to immediately perform the IP address update according to the variation of the IP subnet of the mobile subscriber station, which retains the IP address and is in idle mode, or the foreign agent. Moreover, if data is forwarded while the IP address setting of the idle mode mobile subscriber station is not updated yet, the data is forwarded via an unnecessary path in the network. Hence, resources are wasted.